The present invention relates to a lighting driver circuit that lights a solid state light-emitting element such as a light emitting diode (LED), and a light fixtures that include LED driver circuits.
Conventionally, a lighting driver circuit powering a light source (e.g., an LED) has a power switch supplying a constant current to the solid state light-emitting element. The driver circuit controls ON/OFF operation of the power switch to provide a constant current to and light the solid state light-emitting element at a set dimming level.
For example, in the lighting circuit disclosed in Japanese Patent Application JPA 2011-70966, the lighting circuit controls the ON/OFF switching operation of a switching element in the lighting circuit via a PWM signal whose ON-time ratio corresponds to a dimming control value associated with a dimming level of the light source. Moreover, in this lighting circuit, the switching operation is started and stopped in a first cycle of a half cycle of an AC power source and the ON-time ratio is adjusted in accordance with the dimming control value. That is, in this lighting circuit, a light-emitting diode serving as the light source is illuminated a set dimming level through burst control performed on the ON/OFF operation of the switching element.
Output from a conventional lighting circuit as described above increases in the ON time during which the switching operation is performed and decreases in the OFF time during which the switching operation is stopped, thus causing a ripple waveform in the output voltage and luminance output. The response time of the solid state light-emitting element in particular is faster than that of other light sources (for example, fluorescent light). Therefore a low dimming level or an increase in the cycle (first cycle) of the burst control may cause a visually perceptible variation in the luminance output.